Conventionally, in a hybrid vehicle with one motor 2 clutch power train system, it has been known that, when the engine is started in response to switching request from “EV mode” to “HEV mode” associated with the accelerator opening increase by depressing on the accelerator pedal, engagement of a first clutch CL1 is initiated to be engaged before a second clutch CL2 begins to slip to perform an engine start while slipping the second clutch CL2 (for example, see Japanese Laid-Open Patent Publication No. 2007-69817).
In a hybrid vehicle with a power train system of one-motor, 2-clutch type, in an EV travel or running mode during coasting state with the accelerator being released, for example, during a μ slip control or gear change/shift control, a coast driving takes place sometimes while the state of the second clutch CL2 is in negative slip state. Here, the “μ slip control (micro slip control)” refers to the control in which the second clutch CL2 is slightly slid in order to reduce the friction torque in the EV travel.
However, in a conventional control device of the hybrid vehicle, when there is engine start request, it is configured that cranking of the engine starts immediately upon an engine start request. Therefore, after the cranking start, when the slipping direction of the second clutch changes its polarity from negative to positive, the slip of the second clutch CL2 disappears temporarily by the zero-crossing. There has been a problem of possibility that the variation of the input torque due to the engagement of the first clutch CL1 is not effectively shut off so that an engine start shock may occur.